The present invention relates to systems and methods for systematically effectuating remedial changes to soil and ground water passing therethrough, and more particularly systems and methods that can facilitate the removal and/or transformation of contaminants via targeted ground water migration.
Numerous prior art attempts have been made to facilitate the removal of contaminants from soil. In this regard, the contamination of soils is well-documented and becoming an ever-increasing problem as spills, the dumping of toxic waste, leakage from underground storage tanks and the like continue to occur in increasing frequency, especially with respect to volatile organic contaminants. As a consequence, serious threats to health and wildlife are created as the contaminants introduced into the environment are retained by the subsurface soil and further, can descend hydrodynamically into the ground water.
Several approaches have been developed to facilitate the removal of contaminants. Such approaches have included in situ vapor extraction methods, combustion processes for vaporizing and/or thermally destroying contaminants, electrokinetic soil decontamination (e.g., electroosmosis or electromigration wherein the use of an electric field is applied to selectively attract of facilitate the transport of select contaminants), and—perhaps the most drastic and expensive approach—excavation, isolation and treatment of contaminated soil.
Another approach for removing contaminants from soil have taken the form of super absorbent polymers, either in solid or liquid form, that are capable of being sprayed, pumped or injected in situ wherein the polymer is operative to form a complex with the contaminant and thereafter removed and/or destroyed. Exemplary polymers utilized in such applications include polyethylenes, polypropylenes, polyacrylonitrile, polyesters, alkenyl aromatic resins, silicone polyimides, polyurethanes, natural rubber and synthetic rubber, such as silicone rubbers. Biological approaches to removing contaminants typically involve biodegradation that deploy a population of micro-organisms capable of degrading a specific contaminant sought to be removed.
Still further, biological approaches to removing contaminants have been developed that typically involve biodegradation whereby a population of microorganisms capable of degrading a specific contaminant is deployed in situ. In most cases these organisms are native to the soil and somewhat acclimated to the contaminant. In these cases remediation is facilitated by addition of the proper nutrients to allow these organisms to perform the degradation more rapidly. This is sometimes referred to as enhanced natural attenuation. When organisms are not available in a minority of cases bioaugmentation can be used where organisms are added.
With respect to treating contaminants in the soil subsurface, particularly in subsurface waters, such methods generally fall into four main categories. These are biochemical oxidation, biochemical reduction, chemical oxidation and chemical reduction. The first two of these are collectively called bioremediation when referring to the removal of contaminants using native or augmented microorganisms.
There have been a wide variety of materials and methods used for the bioremediation of contaminants. In many cases materials are injected into the subsurface to facilitate the degradation of the contaminants by providing nutrients and a carbon source for the microorganisms to use in the biodegradation sequence. Lactates, lactate polymers, carbohydrates and oils are among a few of the materials that have been used. In some of the cases the materials are designed to release the carbon source or nutrients over long periods of time to allow the bacteria time to degrade the contaminants and to provide the necessary chemical energy for the bacteria to continue to remediate the contaminants long after the injection as more contaminants flow into the treatment zone. Sometimes these long lasting carbon and nutrient sources are referred to as “barriers’ since they reduce the amount of contaminants that move past the point where the carbon compounds and nutrients are being released. This is not a barrier in the sense of collecting or stopping the movement of the contaminant since the contaminant simply ceases to exist if it is degraded. Unfortunately such barriers rarely have enough microbial activity to remove the contaminant to acceptable levels during the flow through the treatment zone.
In another form of treatment, a physical barrier can be erected such as a “wall.” Exemplary of such form of treatment includes the teachings of U.S. Pat. No. 5,608,137 which teaches a method of containing and remediating contaminants within soil via the steps of placing a gel barrier into the soil for containing the contaminants therein to thus create a containment zone, and thereafter adding microorganisms capable of remediating the contaminants in the soil to the containment zone. This technique, however, is very expensive and adequate containment is difficult to attain. The main idea is that the contaminant flow trapped behind the wall has time to be degraded by the microorganisms before it finds its way around the wall; however, this process is flawed as there is no concentration of the contaminant behind the wall since the water and contaminant are contained together.
There is also a third mode of in situ treatment where solid particles, such as activated carbon, are injected to help slow down the contaminant flow by adsorption on the carbon. The carbon may be also impregnated with bacteria and nutrients to facilitate the reduction of the adsorbed contaminants. A chemical variant on this method is to use emulsions that may provide a carbon source and nutrients to scavenge some of the contaminants and help contain them for future microbial treatment.
Generally speaking, in most of these methods the treatment is chasing the contaminant. In metal wall barriers there is an issue of expense and the purity of the metal required insofar as no metals other than allowable metals, (e.g., iron) are emitted into the ground water as the barrier reacts in water. Along these lines, most iron and especially steels are relatively high in metals that are regulated in ground water.
In the addition of particles such as activated carbon or emulsions the size of the structures are 1,000 times or more greater than the contaminants they are chasing or trying to absorb. The injected particles are trying to fit through pore structures in the subsurface soil that are better traversed and penetrated by the smaller contaminants. For the most part the only effective part of the systems is the carbon sources and sometimes the nutrients that are released as molecules into the subsurface water.
As a consequence, the treatment sought to be deployed in order to eradicate the contaminants is never optimally realized. In this regard, the desired treatments sought to be deployed essentially never “catches up” with the target contaminants and/or the contaminants are not sufficiently contained to a degree that allows for the desired chemical or biodegradation reaction to be optimally realized. Accordingly, there is a substantial need in the art for treating contaminants in soil and subsurface waters that is operative to effectively and efficiently facilitate the removal and/or transformation of contaminants that is easier to deploy, more cost effective and operative to react with the target contaminants to a much higher degree than prior art methods and techniques. There is likewise a need in the art for such methodology that can be tailored to facilitate the removal of a specific type or types of contaminants based upon the unique characteristics of the specific geographical area within which the contaminants are contained. There is still further a need in the art for such contaminant-removal technology that can be systematically deployed to be fluid in nature to thus enable the contaminants to undergo a desired remedial chemical reaction to a degree much greater than prior art methods and techniques.